I agree. I didn't recognize the "cu" because it sounded a lot like "co" in this example!
Native English speaker here. I hear "Cxo" as well. I typed "Cxu" because I have not seen "Cxo" in Esperanto yet; however, I can see how one may be confused.
Mental picture: Dark room, bright light, frightened Duo in handcuffs getting asked "La koko vivas, ĉu?"
Mensbildo: malhela ĉambro, hela lumo, tima Duo en flugilo-mankatenoj, kaj oni demandas al li: "La koko vivas, ĉu?"
It's exactly like in English: • "The chicken's alive, is it?" (="...ĉu?") • "The chicken's alive, isn't it?" (="...ĉu ne?")
The first one expresses surprise that the chicken is still alive. The second sounds like someone who's pretty sure it's alive, and just wants confirmation.
Don't pin me down on this, but I think a rooster would be a virkoko (koko being a prefix that signifies maleness) or kokicxo (cxo is, as I understand it, a commonly used, but unofficial suffix signifying maleness)